1. Field of the Invention
The present invention relates to a composition containing a disease resistance enhancer for plants. The enhancer is produced by using a microorganism, which is environmentally friendly and is safe for users and consumers. The present invention also relates to a method for controlling plant diseases.
2. Brief Description of the Related Art
Pesticides that act directly on a pathogen, such as bactericides, are often used to control diseases that afflict crop plants. However, another type of pesticide is known which control crop diseases by enhancing the plants' intrinsic disease resistance, and these are called “resistance induction-type pesticides.” Pesticides and bactericides that act directly on plant pathogens often exhibit bactericidal effects against the pathogens. Yet, continuous use of such pesticides often results in mutants which are resistant to the pesticide agents. Alternatively, the resistance induction-type pesticides do not act directly on the pathogens and instead control disease infection by inducing the resistance of the plant to the disease pathogen. Hence, there have been no reports to date of mutants that are resistant to this type of pesticide. Furthermore, because the resistance induction-type pesticides have less bactericidal action against organisms, it is more likely that this type of pesticide will be better for the environment, particularly for organisms other than plants.
Pesticides are known which are marketed for induction of resistance to plant diseases, and include probenazole (trade name: Oryzemate), benzothiazole (BTH)-based acibenzolar S-methyl (ASM, trade name: Bion), thiadiazole carboxamide-based tiadinil (trade name: V-GET).
In addition, known substances derived from natural materials which induce disease resistance include polysaccharide decomposition products (JP 5-331016A), cerebrosides (JP2846610B, WO 98/47364 and Koga J. et. al., J. Biol. Chem., 1998, 48, 27, p. 31985-31991), jasmonic acid (JP 11-29412A and Nojiri H. et. al., Plant Physiol., 1996, 110, p. 387-392), chitin oligosaccharides (Yamada A. et. al., Biosci. Biotech. Biochem., 1993, 57, 3, p. 405-409), β-1,3- and β-1,6-glucan oligosaccharides (Sharp J. K. et al., J. Biol. Chem., 1984, 259, p. 11312-11320, Sharp J. K. et. al., J. Biol. Chem., 1984, 259, p. 11321-11336 and Yamaguchi T. et. al., Plant Cell, 2000, 12, p. 817-826), cholic acid (JP 2006-219372A and Koga J. et. al., Plant Physiol. 2006, 140, p. 1475-1483), peptide glycan (Gust A. A. et. al., J. Biol. Chem., 2007, 2007 in press), lipopolysaccharide (Newman M. A, Plant J. 2002, 29, p. 487-495), and the like. These substances are called elicitors and are known to have certain effects, including causing the accumulation of phytoalexins, which have an antimicrobial activity against pathogens, and causing the accumulation of PR proteins (pathogenesis-related proteins), such as chitinase and β-1,3-glucanase, which digest the cell walls of the pathogens and induce hypersensitive cell death (Yamada A. et. al., Biosci. Biotech. Biochem., 1993, 57, 3, p. 405-409 and Keen N. T., Plant Mol. Biol., 1992, 19, p. 109-122).
Furthermore, a method has been reported for controlling infection by pathogens by spraying the supernatant of a proline fermentation solution by Corynebacterium (JP 6-80530A). Yet, the effect of a solution obtained by heat-treating microorganisms under acidic conditions has not been previously reported.